#include <iostream>
#include <vector>
using namespace std;
int main() 
{
    int w = 0, h = 0, cnt = 0;
    cin >> w >> h;
    //cin >> h >> w;
    vector<vector<int>> arr(w, vector<int>(h, 1));
    for (int i = 0; i < w; ++i) 
    {
        for (int j = 0; j < h; ++j) 
        {
            if (arr[i][j] == 1) 
            {
                if (i + 2 < w)
                    arr[i + 2][j] = 0;
                if (j + 2 < h)
                    arr[i][j + 2] = 0;
                cnt++;
            }
        }
    }
    cout << cnt;
    return 0;
}